Field of the Invention
The present invention relates to life estimation circuits and semiconductor devices made using the same, and particularly to a life estimation circuit to estimate the life of a power element and a semiconductor device made using the same.
Description of the Background Art
A power element is subject to repeated, wide temperature variations as a current passing therethrough increases or decreases. As a result of the temperature variations, bonding of wires connecting the power element to electrodes gradually deteriorates and ultimately breaks, causing the power element to reach the end of its life. The wide temperature variations exert stress on solder connecting the components, causing the development of cracking and peeling which will lower the heat dissipation characteristics of the power element, sometimes even resulting in thermal destruction.
However, since a power element is applied to a wide variety of products and used in many different environments, life estimation is extremely difficult. This is problematic because a power element reaches the end of its life while being used, causing an irregular stop of the user side system. If the user does not have the power element in stock, the system needs to be stopped until after a power element becomes available and replaces the one that reached the end of its life, causing a significant loss to the user.
On the other hand, even when the power element is operating normally, some users replace the power element with a new one when the duration of use reaches a predetermined amount of time, so as to avoid abnormalities or failures of the system. In this case, the power element that has not reached the end of its life is discarded, thus increasing the cost of the user side system.
To address this problem, Japanese Patent Laying-Open No. 2015-56415 (Patent Document 1) discloses a life estimation circuit to detect temperature of a power element, count the number of times that the temperature has exceeded a threshold temperature (for example, 50° C.), and when the count value reaches a threshold value, output an end-of-life alarm signal warning that the power element is about to reach the end of its life.